DIYbanter - View Single Post

+++ATH0

On 2019-02-17 15:53, wrote:
About 40 years ago I had a motorcycle ignition problem that was
fixed by replacing the condenser and I never knew why. I still don't
know why Lucas ignitions used a rising field ignition instead of the
usual collapsing field.

Nonsense. This type of ignition is initiated by the points opening and
breaking the primary (LT) current.

The HT voltage achieved depends on the rate of change of primary
current, and failure of the condensor causes the interruption of the
primary current to be much slower because of arcing at the points, which
also wastes energy in the coil which should end up in the spark at the
plug, not to mention destroying the points in hosrt order.

The condensor functions by carrying the primary current for long enough
for the points to separate without an arc being initiated.

If the engine does start and run, the usual symptom of condensor failure
is misfiring at wide throttle openings (when cylinder pressure at the
point of ignition is higher, increasing the breakdown voltage across the
spark plug points) and difficulty starting.